This study proposes to identify factors influencing decision-making regarding genetic testing for Hereditary Nonpolyposis Colorectal Cancer (HNPCC) and the psychological and behavioral outcomes of the testing process. Consenting adults (greater than or equal to 18 years of age) with colon cancer who have either a tumor demonstrating specofoc characteristics (microsatellite instability or MSI+) and/or a positive family history of colon cancer (meeting HNPCC selection criteria) are offered participation in the study through an informed consent session. Those choosing to participate complete a baseline questionnaire. Knowledge, expectations, mood, attitudes, perceived cancer risk, cancer worries, family relationships, spirituality, coping and health beliefs are assessed through the baseline questionnaire.Participants are then provided with an educational session focused on HNPCC, the availability of genetic testing, its risks, limitations and potential benefits, and cancer screening recommendations for families with HNPCC. Following the educational session, participants are provided a counseling session to personally consider gene testing for HNPCC. Following the education and counseling session, participants are presented with a choice of whether or not to undergo genetic testing. Those choosing genetic testing undergo a separate informed consent specifically focused on the process of genetic testing and the potential risks, benefits and limitations of genetic testing. Psychological and behavioral outcomes are reassessed through telephone questionnaire at 6 and 12 months following risk notification or the decision not to undergo testing. For those receiving genetic test results, notification occurs in person along with discussion of available surveillance options. Follow-up counseling and support are provided for all individuals participating in the study. First degree adult relatives of individuals with identified HNPCC germline mutations are also offered participation in the study. To date, 165 individuals have completed baseline testing, 110 individuals have completed 6 month follow-up questionnaires, and 84 have completed 12 month questionnaires and are currently off study. In the process of offering testing to this population, we have collected a growing number who do not have mutations identified however clearly have inherited forms of colon cancer. This finding is leading us to develop a protocol which explores the impact of